According to the prior art, the braking of rail vehicles takes place by way of an electro-pneumatic braking arrangement. The design of such systems is based on the maximum vehicle loading under the assumption of adverse ambient conditions (for example friction value).
Unregulated braking would, for example under partial loading, result in the required deceleration values being exceeded. The adjustment/regulation of the mechanical brake usually takes place by way of a load-dependent variation of the brake pressure.
In the most recent stage of development, permanently excited synchronous machines with separate electric brake circuits are used for driving vehicles, in particular rail vehicles.
Document DE 10 2004 032 680 A1 discloses a motor brake for an electrically driven vehicle, in particular for a rail vehicle, having a permanently excited synchronous machine, with terminals of the synchronous machine being connected via switches to devices which generate a braking torque. Here, it is provided that a capacitor is connected in parallel at least to one of the devices which generate a braking torque, in order to ensure an increased braking power by varying the operating point of the synchronous machine.
The devices which generate a braking torque are for example brake resistances which can be variable.
By connecting a permanently excited synchronous machine in a circuit with ohmic resistances (R) or combinations of ohmic resistances and capacitors (RC), the action of the motor brake is optimized with respect to the rotational speed of the synchronous machine, and it is possible to realize a reliable electric brake, in particular for rail vehicles.
With the described circuit connection of the permanently excited synchronous machine, extremely different boundary conditions, such as for example load state of the vehicle, temperature of the motors and in particular of the magnets, and redundancy requirements, have the result that, for a fixed dimensioning of R or RC, the braking deceleration limit values prescribed by the operator or in standards are not always adhered to.
In the event of a simultaneous activation of all of the provided braking systems, that is to say without controlling intervention, the limit values for deceleration are exceeded in several system states.
Such behavior is not accepted by the operators and prevents the use of a reliable electric brake for rail vehicles.